How to fix OpenVPN error when using network-manager-openvpn-gnome?

I need to connect to some VPN via OpenVPN.

I am using Bionic.

It works when I run the command as sudo from terminal

~$ sudo openvpn --config somevpn.ovpn...Sun Jun 10 22:35:31 2018 TUN/TAP device tap0 openedSun Jun 10 22:35:31 2018 do_ifconfig, tt->did_ifconfig_ipv6_setup=0Sun Jun 10 22:35:31 2018 /sbin/ip link set dev tap0 up mtu 1500Sun Jun 10 22:35:31 2018 Initialization Sequence Completed

without sudo it fails

~$ openvpn --config somevpn.ovpn...Sun Jun 10 22:34:55 2018 ERROR: Cannot ioctl TUNSETIFF tap: Operation not permitted (errno=1)Sun Jun 10 22:34:55 2018 Exiting due to fatal error

Ok, only sudo can create a TUN/TAP device. I added the user to a vpn group and added that group to sudoer

%nm-openvpn ALL=NOPASSWD: /usr/sbin/openvpn

But this only helps on the terminal, that is the user does not need to enter the password when running the command. It does not help when trying to start the VPN connection via network-manager-openvpn-gnome.

network-manager-openvpn-gnome reports a timeout after a few seconds when that vpn connection is activated.

How can I start that vpn connection successfully through the GUI?